Heretofore, there has been known a crane comprising a crane base, a boom attached to the crane base in a raisable and lowerable manner, a jib attached to a distal end of the boom in a raisable and lowerable manner; a hook suspended from a distal end of the jib, and a strut attached to the boom a raisable and lowerable manner to support the jib.
This type of crane is assembled into a workable state in a work area or the like. For example, the strut and the boom are laid down, and in this state, the strut is pulled and raised upwardly with respect to the boom.
As a specific way to pull and raise this strut, it is conceivable to fix a rope to a distal end of the strut, and pull this rope to cause the strut to swing upwardly with respect to the boom. However, a crane equipped with a strut is generally a large-size crane, so that the strut has relatively large overall length and heavy weight. Moreover, in a situation where the strut is laid down, a force can be applied from a height position adjacent to an installation surface of the crane to the strut, only in a direction close to a horizontal direction. Therefore, an extremely large force is required to pull and raise the entire strut simply by pulling the rope at the height position adjacent to the installation surface.
As a measure against this problem, there has been known a technique of raising the strut using an auxiliary crane. For example, JP 2010-241604A (Patent Literature 1) discloses a method of raising a strut of a crane, wherein the strut comprises a base end-side portion located on the side of a base end thereof, and a distal end-side portion located on the side of a distal end thereof and swingably coupled to the base end-side portion. The method comprises: laying down the strut on an installation surface while folding the strut such that a distal end of the distal end-side portion of the strut is oriented toward the base end of the strut; in this state, attaching a rope to the distal end of the strut; and using an auxiliary crane to lifting the rope until the strut is set in a posture where it extends linearly upwardly from the base end thereof.
The strut raising method disclosed in the Patent Literature 1 requires lifting the entire strut by a distance corresponding to a length from the base end to the distal end of the strut, using the auxiliary crane. Thus, it is necessary to prepare a high-performance auxiliary crane having a high withstand load and a long lifting height.